Tigridia pavonia

Hell All,
Is Tigridia pavonia heat-sensitive? I planted a bunch bought at a local
nursery in a 5-gallon pot in April. I set the pot inside a Talavera
ceramic turtle (yes, it has a drain hole, and yes, it looks like the
1960s) which shaded the black plastic from the sun.
They came up and looked wonderful in a spot with a few hours of sun. They
grew strongly, leaves about 2 feet tall, until we reached the 110 degrees
F phase of our summers, and suddenly in one day the leaves turned light
brown. The soil was still moist.
I put the pot in full shade. There are only a few alive; most, when I tug
on the leaves, just come out and appear rotten.
What did I do wrong?
Thanks,
Leo Martin
Phoenix Arizona USA